A High Resolution Picture of the Intracluster Gas

Abstract

Chandra has significantly advanced our knowledge of the processes in the intracluster gas. The discovery of remarkably regular ``cold fronts'', or contact discontinuities, in merging clusters showed that gas dynamic instabilities at the boundaries between the moving gases are often suppressed, most likely by specially structured magnetic fields. Cold fronts are not limited to mergers -- Chandra observed them in the cores of more than 2/3 of the cooling flow clusters, where they often divide the cool central and the hotter ambient gas phases. The natural state of the low-entropy central gas in clusters thus appears to be to slosh subsonically in the central potential well, with several interesting implications. Hydrostatic equilibrium is not reached and the hydrostatic total mass estimates cannot be valid at small radii (r<100 kpc). The kinetic energy dissipated by the sloshing gas may be sufficient to compensate for radiative cooling. In the absence of a recent merger, the cause of such sloshing is unclear. It might be related to the mechanical energy generated by the central AGN, evidence of which (the bubbles) is also observed by Chandra in a large fraction of the cooling flow clusters. Heat conduction across cold fronts is suppressed completely. In the bulk of the gas, it is reduced by a factor of ~10 or more relative to the classic value, as shown by merger temperature maps. A spatial correlation between the gas temperature maps and the radio halo maps is observed in several mergers, which may provide clues for the relativistic particle acceleration mechanisms.